Table 1. Levels of evidence: classes of recommendation.

		Definition		Phrasing
Level of evidence
	A	Clear evidence for the recommendation
			Clearly proven through multicenter RCTs or meta-analysis with adequate content and power with high generalizability of findings
	B	Reliable evidence for the recommendation
			Evidence found through well-performed cohort or patient-control group studies
	C	Possible evidence for the recommendation
			Not reliable, but relevant evidence found through small RCTs, observational studies, or case series
	E	Expert opinions
			No supporting evidence, but expert opinions based on clinical experience and expertise
Classes of recommendation
	Class I	Clear evidence (A) and benefits, and high applicability in practice		Recommended
	Class IIa	Reliable evidence (B) and benefits, and high or moderate applicability in practice		Should be considered
	Class IIb	Unreliable evidence (C or D) and benefits, but high or moderate applicability in practice		May be considered
	Class III	Unreliable evidence (C or D), may cause harm, and low applicability in practice		Not recommended

RCT, randomized controlled trial.